#include <stddef.h>

struct flex_array_struct{
    int num;
    int data[];
};
void func(void){
    struct flex_array_struct flex_struct;
    size_t array_size=4;
    /* Initialize structure */
    flex_struct.num = array_size;
    for (size_t i = 0;i < array_size;++i){
        flex_struct.data[i]=0;
    }
}